if you push firmly with your foot and hold it there, does it eventually click into 3rd? or does it never go into 3rd, act like a second nutural, then go into 4th?
in either case, if its under warranty, take it to the dealer ASAP.. the problem with trans issues is you have to split the cases to look at it. you cant fix anything from the outside.
its possible for Honda to warranty you a brand new motor if you do have a trans issue.